Ok, its down to personal choice. You need to consider -
a) the desired effect - do you want your quilt to be flat or do you want more loft?
b)What is it going to be used for? - is it going on a wall or is it going to be used on a bed or is it a cuddly blanket?
c) the budget
d) how are you going to quilt it
You then need to know a bit about each main type of wadding available -
Almost all the modern waddings are made in just a couple of factories in Texas.
Polyester Wadding - eg Hobbs Polydown, Sew Simple Polyester, Dream Poly, legacy by pellon etc
Usually the cheaper option, great for charity quilts too.
Poly does not breath - it sweats, so if its for your bed, this may not be the best option. Virtually no shrinkage. Produces a slightly more 'stiff' result.
Hobbs Thermore is very thin, orgionally designed for clothing, but is great for hand quilting.
80/20 -eg Hobbs 80/20, Sew Simple 80/20
Probably the most popular type. Great for tops which are not pieced very precisely.
Good loft - which can help disguise problem areas.
Cotton - eg Sew Simple, Warm & natural, Hobbs 100% Cotton etc
Cotton creases and may not keep its shape as well as some others - therefore its not great for wall hangings. It also has the most shrinkage, but it is very cuddly. When quilting it may beard. If so try a polyester thread rather than cotton.
For machine or longarm quilting the smoothside goes towards the back, but for hand quilting its the other way. See Scrim below
Wool eg Hobbs Wool, Sew Simple Wool etc
More expensive, but does not crease. Wool breathes, it does not sweat. Gives warmth but disperses excess heat well. Good loft.
Luxury feel, more expensive. Light and warm.
Does not crease.
Often sold as being 'green', but the process involves breaking down the bamboo canes with caustic soda. My personal experience of bamboo so far is not good - the quilt turned out very stiff and hard. Other quilters have reported that the bamboo fibres break down after several washes.
Plastic recycled Bottles - eg Dream Green
Nice and soft and cuddly, although feels a bit plastic. Little or no shrinkage.
What is Scrim?
Scrim is like an interfacing, it holds the layers together and helps keep its shape. You often find cotton wadding with or without Scrim. - my personal advise is not to buy cotton wadding without scrim.
Very Light Coloured tops
Look for a beached or pale coloured wadding.
Double layers of waddings
Many quilters use double layers of waddings - often mixing them for different effect. Very common when more loft and dense quilting are going to be required.
Joining Wadding Together
Several companies has brought out joing tape which enables you to stick two pieces of wadding together.
Personally, if I need to join wadding I use a large zig zag stitch and butt both edges of the wadding against each other and join together this way.
Can I use a sheet instead of backing fabric? Another very common question.
I would recommend that you don't do this. Sheets have a very high thread count and it is more difficult to quilt. its too tight and it may also cause bearding.
Patchwork fabrics and quilt backing fabrics have a less dense thread count to enable quilting and to work well with todays modern waddings.
What about Batik?
In general batik fabrics are quite densly woven and these would not be a great choice for backing.
SewBatik and a couple of other companies do a great range of extra Wide Batik Backings, and these are specially manufactured so are of the correct thread density for backing your quilts.
Can I use patchwork Fabric?
Yes of course, but you may find that you need to join this on larger quilts. If you do it is important that you remove the selvedges for the joining seam as this will contract inside the quilt. The joining seam needs to be wide - generally recommend around half inch and press open.
Extra Wide Backing Fabrics
These are generally 108 inches wide and are fantastic as they save the need to have a join in your quilt backing. They can be 100% cotton or brushed cotton /flannel.
This can also be used as a backing fabric and produces a cuddly soft back and a quilt which is light but warm.
Double sided minky is also great and both can be used with or without wadding.
I have a range of wadding and extra wide quilt backings in my shop....here is the link http://www.quiltsandwich.co.uk/#!shop/c50p